How can I join two tables and use aggreagate function in one LINQ query

I want to merge two tables where in one table is scores and in another table are i开发者_如何学Gonformation about for example article.

Tables:

Articles
---------------
article_id
title
date
category
user_id

Articles_Scores
---------------
article_id
user_id
score

I already write this linq query:

from p in db.Articles.Where(p => p.user_id == 2)
join o in db.Articles_Scores.Where(o => o.user_id == 2) on p.article_id equals o.article_id
group o by o.article_id into result
select new
{
result.Average(m => m.score)
};

How can I select the other fileds. Why I cant use p in select? Can someone tell how should I do this to get following results:

article_id  title   date    category    score

from p in db.Articles.Where(p => p.user_id == 2)
select new
{
    p.article_id, 
    p.title, 
    p.date, 
    p.category,
    AverageScore = db.Articles_Scores
                     .Where(o => o.user_id == p.user_id && p.article_id == o.article_id)
                     .Average(m => m.score)
}; 

I suggest that you join them in DBML designer and use this:

var query = (from article in articles
            where article.article_id == givenId && article.user_id == givenUser
            let scores = article.scores.ToList()
            from score in scores
            select score.value).Sum();